In general, electronic systems that may require a wide and an accurate output power control range employ both open loop mode (i.e., without feedback), as well as closed loop mode (i.e., with feedback), for power control due to range limitations of detector diodes. Typical single and dual detector diode circuitries may provide a power measurement range of 30-35 dB. A detection circuitry with multiple detector diodes provides a wide power range; however, the complexity of such a circuitry may lead to inaccuracies and may be cost intensive.
In systems where accurate power steps may be required in both open loop and closed loop modes, usually a standard power control loop (PCL) may be used in the closed loop region and therefore a continuous power control transition between the two modes is required. If there is a difference between measured and reference signals during transition from the open loop mode to the closed loop mode, the standard PCL may immediately react to minimize the difference; however, this may cause an inaccurate power step across the transition boundary of the two modes. This error is caused by the original open loop estimation. This may lead to additional problems such as switching issues or spectrum widening.
The error during power transition from the open loop mode to the closed loop mode can occur, for example, in a communication device, such as a cell phone. For example, a base station may require a mobile station to transmit low output power in an open loop mode. In such a case, the mobile station may come to know of a difference between the measured signal and the reference signal only during transition from the open loop mode to the closed loop mode.
To avoid such a problem, in existing systems a slot-to-slot transition between the open loop mode and the closed loop mode is used (i.e., a single mode is selected at a particular time slot boundary). Loop state estimates, such as open or closed loop differences are sent back to a decision making block, which pre-determines a slot boundary at which the loop state is to be changed. This process may be used such that power steps at a particular slot boundary occur in only one of the modes (e.g., open or closed modes). Implementation of such a process requires intelligence and decision-making capabilities, as well as calculations to minimize step errors, normally during baseband processing, in addition to having prior knowledge of the direction of power change.